The flash point of styrene-containing unsaturated polyester resins and other free radical curing resins containing styrene as monomer such as vinyl esters and urethane acrylates is very close to 32.degree. C. This is the temperature below which materials are classified as "Highly Inflammable" according to the British Highly Flammable Liquids and Liquid Petroleum Gases Regulations 1972. Such resins are therefore subject to storage and transport conditions laid out in the Regulations. Moreover the use of such resins in high risk areas e.g. mines is not desirable.
It is possible to replace the styrene monomer in these resins by other monomers and such monomers include diallyl phthalate, ethylene glycol dimethacrylate, bromostyrene, vinyl toluene, chlorostyrene, t-butyl styrene and p-methyl styrene. In fact resins based wholly on bromostyrene do not burn in the liquid state. (GB No. 1,569,070). However some of these monomers are not commercially available on a large scale or are not economically viable whilst others such as diallyl phthalate will not undergo cold cure. Ethylene glycol dimethacrylate yields resins of much higher viscosities than are desirable. The partial replacement of styrene by these alternatives monomers is not successful as the vapour pressure of styrene is the controlling factor in determining the flash point and the flash point of mixed monomer systems is always close to that of the most volatile monomer present.